As stipulated in the Long Term Evolution (LTE) specification, a measurement control information transmitted from an evolved NodeB (eNB) to a User Equipment (UE) is composed of the following items:
measurement objects, each of which corresponds to a frequency for an Evolved UMTS Terrestrial Radio Access Network (E-UTRA) and a Universal Mobile Telecommunication System (UMTS) and a set of frequencies for a GSM/EDGE Radio Access Network (GERAN) and is provided with a separate number (obj-id);
measurement reporting configurations, each of which corresponds to a measurement reporting criterion and a set of parameters, and is provided with a separate number (report cfg-id); where, a specific reporting criterion includes event triggered reporting, periodical reporting and event triggered periodical reporting; and for example, there are report events A1, A2, etc.; and
measurement identities (meas-id), each of which associates uniquely a measurement object with a measurement event and is included in each measurement report from the UE.
A specific instance is presented as follows.
1. A UE is configured, from a network, with three measurement objects with respective numbers (obj-id) of 1, 2 and 3 and with respective correspondence to E-UTRA f1/f2/f3
2. The UE is configured, from the network, with two measurement reporting configurations with respective numbers (report cfg-id) of 1 and 2, where an event A1 and a corresponding set of configuration parameters are used for the first measurement reporting configuration 1, and a periodical reporting criterion and a corresponding set of configuration parameters are used for the second measurement reporting configuration 2.
3. The UE is configured, from the network, with two measurement identities:
the first measurement identity (meas-id=1) associates the first measurement object (obj-id=1, E-UTRA f1) with the first measurement reporting configuration (report cfg-id=1, i.e., A1); and
the second measurement identity (meas-id=2) associates the third measurement object (obj-id=3, E-UTRA f3) with the second measurement reporting configuration (report cfg-id=2, i.e., the periodical reporting criterion).
4. Thus, the UE will indicate in a measurement report that the measurement report is currently triggered by the measurement identity (meas-id=1) upon determining that E-UTRA f1 satisfies the configured event A1.
The foregoing measurement control information is a part of the contents in a Radio Resource Control (RRC) message for which it has been stipulated in the standard that the UE shall store the respective measurement control information received in its own measurement context (Var Measurement Configuration) referred here to as a UE-side measurement context in order to control the UE. Also a corresponding measurement context referred here to as a network-side measurement context shall be stored at the currently serving eNB in order to perform delta measurement configuring on the UE, and the UE-side measurement context and the network-side measurement context shall be kept consistent in contents.
As stipulated in the current LTE specification, the UE has to perform the following “exchange operations” on its own stored measurement context for inter-frequency switching or for inter-frequency RRC connection reestablishment:
a) all the measurement identities associated with measurement objects corresponding to destination frequencies are located and then associated onto measurement objects corresponding to source frequencies; and
b) all the measurement identities associated with the measurement objects corresponding to the source frequencies are located and then associated onto the measurement objects corresponding to the destination frequencies.
The source and destination frequencies as referred here to are defined as follows.
1. For inter-frequency switching, the source frequency refers to the frequency of a cell where the UE resides prior to switching, and the destination frequency refers to the frequency of a cell where the switched UE resides after switching.
2. For inter-frequency RRC connection reestablishment, the source frequency refers to the frequency of a cell where the UE resides prior to RRC connection reestablishment, and the destination frequency refers to the frequency of a cell where the UE resides after the UE performs RRC connection reestablishment successfully.
To prepare for inter-evolved NodeBs (eNB) switching, a source base station may transmit to a destination base station its own stored UE context (AS-Configuration) including a network-side measurement context (source Measurement Configuration) as described above and also part of system information (MIB/SIB1/SIB2, where MIB stands for Master Information Block, and SIB stands for System Information Block) of a cell where the UE currently resides as well as carrying frequency information.
Generally the base station where the UE currently resides in a connected status maintains a UE context including the measurement context. The base station typically can generate desired RRC configuration information only from configuration information of its own currently stored UE context to control the UE, and after it is transmitted to and successfully confirmed by the UE, the base station shall also modify correspondingly its own stored UE context. In this way, the context stored internal to the base station can be synchronized all the time with that stored at the UE side to facilitate a subsequent control process.
When inter-frequency switching or inter-frequency RRC connection reestablishment occurs with the UE, the measurement context is updated, i.e., the foregoing exchange operations are performed, at the UE side as stipulated in the standard. In order to maintain synchronization of the UE network-side measurement context with the UE-side context, a corresponding process also has to be performed at the network side. However for inter-eNB switching or reestablishment scenario, a drawback of the prior art lies in that whether the desired process at the network side is performed by the source base station or the destination base station has not been ascertained in the existing standard, which may result in a lack of synchronization between the UE-side measurement context and the network-side measurement context after switching or reestablishment and consequently influence a subsequent control process.
The drawback of the prior art is present not only in a base station (eNB) of an LTE system but also in a radio relay node of an LTE-A system in processing the context, where LTE-A stands for LTE Release 10.